Electric control motors have been used for the positioning of control equipment such as dampers, valves, and other types of regulating equipment. Normally these motors utilize a conventional electric motor and gear reduction to drive an output shaft which has an angular rotational limit of less than 360.degree.. More typically the angular rotation is limited to the range of 90 the use to 160 rotational degrees. These motors generally utilized fixed limit switches to establish the number of rotational degrees that the motor will be allowed to operate within. When a motor utilizing a fixed degree of rotation is utilized, it is necessary to connect the motor to different types of loads by the use of varying types of crank arms or linkages that have to individually be adjusted for the number of degrees of rotation of the motor shaft and the amount of movement required of the load.
In more recent years, it has become common to provide control motors that have an adjustable stroke or number of rotational degrees. The adjustable stroke type motors normally have an adjustment range of 90 to 160 rotational degrees in order to provide the most convenient application of the motor to various loads. For example, an air damper in a duct, usually utilizes a 90.degree. rotation from its full open to its full closed position. In some cases, such as in the operation of a valve, the rotation of 90.degree. may not be adequate to completely operate the valve. In that case a longer stroke is necessary.
Where a single motor is used on varying types of applications, the stroke can be changed by the use of different types of linkages. This is very expensive and time consuming. It is also possible to provide control motors that have varying stroke lengths that are adjustable by mechanically positioning the limit switches. In this case the motor must be constructed so that the limit switches are readily accessble to the installer, and are accessable moveable in position around the output shaft. Other types of variable stroke motors have been provided wherein the variation in stroke length is accomplished by setting a potentiometer which is in a circuit that controls the electronics or electric circuit operating the motor.
It has been recently found that where adjustable stroke motors using a stroke adjusting potentiometer are used, that occasionally a malfunction of the electrical control circuit can cause the motor to rotate more rotational degrees than are desirable. This causes damage to either the motor or the load, and it is, therefore, desirable to also position a limit switch at the same point of rotation as that established by the use of a potentiometer in setting the stroke for the motor. This could be conceivably accomplished by providing a motor with separate adjustments of a stroke adjustment potentiometer and a limit switch. This type of arrangement, wherein two separate adjustments are necessary, leads to complication and expense in the installation.